Radio Frequency Life Detection Radar System

ABSTRACT

Trapped or confined individuals may be located and rescued by detecting their vital signs (e.g., chest movement or heart beat) using reflected, radio frequency signals over a range of multiple antenna polarities.

RELATED APPLICATION

This application claims the benefit of priority from U.S. ProvisionalApplication No. 62/924,110 (the “'110 Application”) filed Oct. 21, 2019.This application incorporates by reference the entire disclosure of the'110 Application as if set forth in full herein.

INTRODUCTION

This section introduces aspects that may be helpful to facilitate abetter understanding of the described invention(s). Accordingly, thestatements in this section are to be read in this light and are not tobe understood as admissions about what is, or what is not, in the priorart.

Major natural disasters, such as earthquakes, tsunamis or storms willlikely cause infrastructure damage leading to injuries, significant lossof life, and people trapped beneath debris. Typically, immediate searchand rescue operations are required in order to save lives because thedifference between life and death could be a matter of hours. It istherefore essential for first responders to have a clear understandingof the location and health status of injured and/or trapped individuals.To ascertain such information first responders implement so-called “lifedetection” techniques such using trained search dogs, radar, optical,acoustic, and infrared life detection systems. In general, lifedetection systems can be divided into two different categories: activeand passive sensing. Search dogs, optical, acoustic and infrareddetection systems rely on passive sensing. Typically, passive sensingsystems only measure energy or signals that have been transmitted froman external source such as the temperature of a trapped individual.

In comparison, an active sensing system, such as a radar-based detectionsystem, transmits its own source of energy by actively sending a wave ofelectromagnetic energy towards a target (e.g., trapped individual) andthen detecting the amount of backscatter (portion of the originallytransmitted signal) that is reflected by an individual, for example,back to the active system.

Generally, existing radar systems rely on multiple transmitter-receiverantenna pairs that are displaced from each other to enable the detectionof multiple targets in three dimensions (3D). This need for multipletransmitter-receiver antenna pairs and physical antenna displacementresults in large, complex, heavy and expensive equipment. Further,existing radar detection systems only operate effectively over shortdetection range, have poor multi-target identification and poorpositioning capabilities.

Accordingly, it is desirable to provide systems, devices and relatedmethods that overcome the shortfalls of existing techniques.

SUMMARY

The inventors disclose various systems, devices and related methods thatmay be used to detect individuals, for example, that are trapped beneathcollapsed structures or trapped within confined spaces, for example.

One exemplary method may comprise: transmitting radio frequency signalstowards a trapped or confined individual from a fixed, rotatingtransmitter; changing the polarity of one or more of the transmittedsignals; receiving one or more reflected signals from the trapped orconfined individual at one or more rotating receivers, each reflectedsignal corresponding to a transmitted signal; and completing ashort-time Fourier transform and time frequency analysis to detectmovement of the trapped or confined individual based on the receivedsignals.

DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a simplified block diagram of an exemplary, inventivesystem according to an embodiment of the invention.

FIGS. 2A and 2B depict exemplary positions of an inventive antennaaccording to embodiments of the invention.

FIG. 3 depicts an exemplary flow diagram of a multi-target detection andlocalization process according to an embodiment of the invention.

FIG. 4 depicts an exemplary, experimental radar system according to anembodiment of the invention.

FIG. 5 illustrates the principals of ranging of a radar.

FIGS. 6A to 6C depict experimental results produced by an inventivesystem.

FIG. 7 depicts exemplary detection of micro-Doppler frequency shifteffects using an inventive system according to an embodiment of theinvention.

DETAILED DESCRIPTION, WITH EXAMPLES

Exemplary embodiments of systems, devices and related methods fordetecting individuals that are trapped beneath rubble, for example.

Embodiments of the invention are described herein and are shown by wayof example in the drawings. Throughout the following description anddrawings, like reference numbers/characters refer to like elements.

It should be understood that although specific embodiments are discussedherein, the scope of the disclosure is not limited to such embodiments.On the contrary, it should be understood that the embodiments discussedherein are for illustrative purposes, and that modified and alternativeembodiments that otherwise fall within the scope of the disclosure arecontemplated.

It should also be noted that one or more exemplary embodiments may bedescribed as a process or method (the words “method” or “methodology”may be used interchangeably with the word “process” herein). Although aprocess/method may be described as sequential, it should be understoodthat such a process/method may be performed in parallel, concurrently orsimultaneously. In addition, the order of each step within aprocess/method may be re-arranged. A process/method may be terminatedwhen completed, and may also include additional steps not included in adescription of the process/method if, for example, such steps are knownby those skilled in the art.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. As used herein, the singularforms “a,” “an” and “the” are intended to include the plural form,unless the context and/or common sense indicates otherwise.

It should be understood that when an system or device, or a component orelement of a system or device, is referred to, or shown in a figure, asbeing “connected” to (or other tenses of connected) another system,device (or component or element of a system or device) such systems,devices, components or elements may be directly connected, or may useintervening components or elements to aid a connection. In the lattercase, if the intervening systems, devices, components or elements arewell known to those in the art they may not be described herein or shownin the accompanying figures for the sake of clarity.

As used herein the term “operable to” means “functions to” unless thecontext, common sense or knowledge of one skilled in the art indicatesotherwise.

It should be understood that the phrase “computer” and“micro-controller” may comprise one or more electronic processors thatare operable to retrieve and execute instructions stored as electronicsignals in electronic memory, where a set of such stored instructionsmay constitute steps in an inventive process or application, or may beexecuted to complete an inventive function(s) such as rotating,transmitting, receiving, sending, processing, detecting, completed,displayed, sensing, re-processing, re-computing (and tenses of theaforementioned functions) to name just a few inventive functions thatmay be completed by executing such stored electronic instructions.Further, it should be understood that each embodiment of a computer ormicro-controller described herein is further configured with thenecessary hardware and firmware components to enable each to processsignals and data and/or content (collectively “data”) much faster thanhumanly possible and to receive, transmit and exchange data much fasterthan humanly possible. Each of the embodiments of the present inventioncannot practically be implemented in any amount of time that would beacceptable to one skilled in the art using human beings as substitutesfor the systems and devices described herein. For example, theembodiments described herein involve methods that detect the vital signsof individuals, for example, that may be trapped beneath collapsedstructures or are trapped within a confined space. Accordingly, the useof humans as substitutes for such methodologies is contrary to theobjectives of the invention and does not result in the improvementsprovided by the invention because, for example, the inventivemethodologies process received, reflected signals many times faster thanthe human mind (within the time periods demanded by users of embodimentsof the present invention and those skilled in the art of the presentinvention).

As used herein, the term “embodiment” or “exemplary” mean an examplethat falls within the scope of the invention(s).

To overcome the disadvantages of existing radar detection techniques thepresent inventors provide for, among other things, the use of a singletransmitter-receiver pair instead of multiple pairs.

Referring now to FIG. 1, the inventors provide for an inventive,exemplary radar-based life detection system 1 that includes a singlerotary, transmitter-receiver antenna pair. By rotating the system 1,multiple polarities with spatial antenna displacement may be used inorder to achieve multiple target detection and localization in 3dimensions (3D) along with the ability to measure the breathing andheartbeat of trapped individuals, for example.

The exemplary system 1 may comprise a portable, accurate, and affordablelife detection system. In embodiments of the invention, the system 1 maybe a handheld device, or a device that is mounted on a drone or a mobilerobot to name just some of the configurations of the exemplary system 1.

In one embodiment the system 1 may comprise a special purpose computer100 operable to execute instructions stored in a memory to monitor,control, and perform required signal processing for multi-targetdetection, 3D localization, and vital signs detection using radiofrequency (RF) signals, for example. To complete each suchfeature/function the computer 100 may execute instructions stored inmemory, that include, for example, Artificial Intelligence (AI), machinelearning and/or deep learning detection processes. In an embodiment,such a process may take the form of stored instructions that completethe steps of one or more neural networks.

Yet further, the system 1 may be separated into individual components.For example, in one embodiment the computer 100 may be located remotelyfrom other components (e.g., subsystems) of the system 1. In such aconfiguration the computer may using wired or wireless communicationssuch as Wi-Fi, cellular networks (5G for low latency), Bluetoothwireless technology using one or more RF communication protocols.

The exemplary system 1 may also comprise a thermal imaging device 104and microphone array 105 that may be interfaced with the computer 100.Devices 104, 105 may function as secondary and tertiary life detectionsystems when used in combination with other features of system 1 inorder to increase the accuracy and detection capability of the system 1.

In another embodiment, system 1 may comprise electronic circuitry thatfunctions as an interface to connect computer 100 with a drone and/ormobile robot controller system 111. Such a system 111 may be operable toprovide feedback and control signals to system 1 in order to aid in asearch and rescue operation.

System 1 may comprise a display 101 that may be an integral part ofcomputer 100, for example, or may be a separate component (not shown).In either case, the display 101 may be operable to display the resultsof a search and rescue operation and/or control features of the system1. In an embodiment the computer 100 may execute stored instructionsthat function as a graphical user interface (GUI). Features of the GUImay be displayed in order to display the results of a search and rescueoperation and/or control features of the system 1, for example.

In another embodiment, results may be sent to an augmented realitydevice and/or wearable glasses/head units (not shown) where the resultsmay be overlaid, for example, on an image from a camera.

Referring back to FIG. 1, a field-programmable gate array circuitry 102(FPGA) may function as an interface between RF front-end circuitry 109and the computer 100. In an embodiment, the FPGA may be responsible forgenerating different RF transmission signals to, and high-speed captureand processing of received (reflected) signals from, the RF front-endcircuitry 109. The FPGA 102 may also comprise flash EEPROM and RAMmemory 102 a (e.g., 1 Gigabit)) that may function to store signals,data, and image processing instructions for accurately locating objectsor persons as a part of a search and rescue operation. The FPGAcircuitry 102 may also be interfaced with a micro-controller 103 (e.g.,200 Megabits per second). In an embodiment, micro-controller 103 mayperform general “housekeeping” functions, such as data collection, andcontrol of various other subsystems. It should be understood that theFPGA 102 and flash/memory 102 a may be a separate subsystem of system 1or, alternatively, may be a part of RF front-end circuitry 109, forexample.

In exemplary embodiments, FGPA 102 may generate exemplary Inputfrequencies from 300 MHz to 8 GHz as well mixer demodulated IFfrequencies and may apply one or more modulation schemes, such ascontinuous wave (CW)-modulation (or unmodulated), frequency and pulsemodulation/unmodulated (compressed and/or uncompressed), Intra-pulse orinterpose modulation, linear frequency modulation, and/or chirpedfrequency modulation, for example.

In more detail, the micro-controller 103 may be operable to executestored instructions to communicate with the computer 100 and the FPGA102 in order to control various subsystems and exchange data with suchsubsystems, for example. For example, micro-controller 103 may beoperable to exchange instructions (e.g., electrical signals) with amotor controller 110 c in order to adjust the rotation of an antennarotary mast 110. Further, the micro-controller 103 may be operable toreceive data representative of the rotational position of the mast 110from a rotary encoder 110 d that is connected to the mast 110. Stillfurther, data from a gyroscope 107 and an accelerometer 108 may also bereceived by the micro-controller 103. Thereafter, the micro-controller103 and/or computer 100 may be operable to execute instructions storedin memory to adjust the orientation of the mast 110 due to unwantedmovement and vibrations of the system 1 in accordance, for example, withone or more stored processes realized in stored electronic instructions(e.g., target detection processes).

In an embodiment, if the system 1 is to be operated by a live operatorin a “handled” mode, a wireless or wired smart sensor (not shown inFIG. 1) may be placed on the operator to collect vital signs such asheart rate and breathing rate in order to filter out signal interferencethat may cause data collection errors.

Continuing, global positioning system (GPS) circuitry 106 and a GPSantenna 106 a may, in combination, be operable to provide globalpositioning and accurate timing for system-wide clock distribution andsynchronization to the micro-controller 103 and the RF front-end 109.

In an embodiment, RF front-end 109 comprises RF analog-to-digital (ADC)109 b, 109 c and digital-to-analog (DAC) 109 a conversioncircuitry/components for automatic gain control of transmitted signalsover a wide range of RF power outputs. Digital signals generated by theFPGA 102 may be converted to analog signals through a DAC circuitry 109a, passed through a signal splitter 109 h, and then transmitted to anarea to be analyzed (e.g., for indications of individuals that are aliveor moving) via antenna 110 a and to be fed into an electronic mixer 109i.

Signals sent from the transmitting antenna 110 a towards a target (e.g.,a trapped or confined individual) may be reflected by a target (e.g.,possible individuals) and received by the receiving antenna 110 b. In anembodiment, the system 1 may comprise a receiver or transceiver operableto receive frequencies over the range of 300 MHz to 80 GHz, for example,and have a dynamic range of 120 dB, for example. The received signal(s)may then be amplified by a low-noise amplifier 109 k and then split by asignal splitter 109 j. One path of the split signal may be fed into themixer 109 i and mixed with the transmitted signal from splitter 109 h.When two signals (e.g., frequencies) are applied to the frequency mixer109 i the mixer 109 i may be operable to produce a new signal(s)representing the sum and difference of the original frequencies. Theoutput of the mixer 109 i may then be passed through a base bandamplifier 109 e which filters out portions of the frequencies thatrelate to the sum of the original frequencies while allowing thedifference of the original frequencies (beat frequency) to pass through.In an embodiment, this passed through signal may be an analog signalthat is converted to digital form by an ADC 109 b and then sent to theFPGA 102. The so converted signal may be further converted to a valuethat is processed in accordance with a target detection process. Theother path of the signal splitter 109 j may represent the originalsignal that was received by the receiving antenna 110 b which may bepassed through amplifier 109 f, converted to digital form via ADC 109 cand then sent to the FGPA 102 where a value of the so-converted signalmay be processed in accordance with an inventive target detectionprocess.

In an embodiment, timing and clock distribution circuitry 109 d may beoperable to provide synchronization and coherence to transmitted andreceived signals used by the DAC 109 a, ADCs 109 b, 109 c, and mixer 109i.

It should be understood that the RF front-end 109 may alternatively beimplemented in software stored as instructions (electrical signals)and/or with additional transmission and receiving paths for additionaltransmitting and receiving antennas.

The rotary antenna mast 110, 200 may house the transmitting antenna 201and receiving antenna 202. In embodiments of the invention, the system 1provides multiple antenna positions and antenna polarities 205 byrotating the mast 206 from 0 to 360 degrees, for example. Inembodiments, the mast may be controlled and rotated by the computer 100or micro-controller 103 such that the rotational speed of the mast mayvary. For example, the amount of electrical or physical interferencewithin a reflected signal and/or the accuracy needed to positivelydetect a trapped individual may determine whether the speed of the mastmay be increased or decreased, for example.

Yet further, the speed of the mast may be controlled such that the mastrotates at a pre-determined speed initially (e.g., a first mode ofoperation). Thereafter, the speed of the mast may be reduced (i.e., asecond mode of operation) when a potential target has been located.Still further, another mode of operation may allow the polarity of thesignal being transmitted from the mast to be varied.

As shown in FIGS. 2A and 2B, in an embodiment the transmitting antenna201 may be located at the center of the mast 206 and its position fixedwhile its polarity may be continuously changed between a vertical 204and horizontal 203 polarity. In contrast, the receiving antenna 202 maybe off-centered and located toward the edge of the mast 206 where bothits position and polarity may continuously change between vertical 204and horizontal 203.

In an embodiment, by rotating and displacing the antenna multiplevantage points for the receiving antenna are created. Thus, the rotatingantenna can be said to “mimic” multiple, physical receiving antennas.

In an alternative embodiment, a secondary receiving antenna 207 at adifferent polarity and location compared to the first receiving antenna202 may be utilized to provide better detection and accuracy. Thus, oneor more rotating receiving antenna may be used.

The configuration, location, and orientation of the transmitting antenna201 and receiving antenna 202, 207 may be different, as illustrated inFIGS. 2A and 2B. Because RF signals propagate differently throughobstacles (e.g., human beings) at different polarities, the ability forthe inventive system 1 to sweep through a plurality of RF/antennapolarities in order to detect a trapped individual, for example, isadvantageous.

In an embodiment, to determine the location of a trapped individual, thereceived, reflected signals may be processed in accordance with amulti-target detection and localization process that may be implementedby computer 100 and FGPA 102. The inventive process detects multipletargets (trapped individuals) and their vital signs (heartbeat,breathing) with 3D localization using multiple RF signal profiles anddifferent antenna positions and polarities through, among other things,data provided by the rotary antenna mast 110. The system 1 may usemultiple RF signal profiles, i.e. continuous wave (CW), frequencymodulated continuous wave (FMCW), pulsed, random noise and/or anycombination of such profiles.

FIG. 3 illustrates exemplary features and steps in such an inventiveprocess. The exemplary process illustrated by FIG. 3 may begin byestablishing communications between the computer 100 and othersubsystems and then initializing the antenna rotary mast 110 to azero-degree rotational position.

A first RF signal profile (signals having a range of frequencies,modulations, polarities, for example, 300 MHz to 80 GHz and one or moremodulation schemes such as CW modulation or unmodulated, frequency andpulse modulation/unmodulated (compressed and uncompressed), intra-pulseor interpose modulation, linear frequency modulation, and chirpedfrequency modulation) may be transmitted by the FPGA 102 towardssuspected targets (e.g., trapped individuals) using the RF front-end 109and the transmitting antenna 110 a. The so-transmitted RF signalspropagate through the air until a target is reached, whereupon thetarget may reflect a portion of the signal back towards the receivingantenna 110 b. Upon being received, the reflected signal(s) may be sentto the FPGA 102 through the RF front-end 109. This signal and otherdata, such as the rotary encoder position, GPS data/clock, gyroscope,and accelerometer data may then be received and stored by themicro-controller 103 (collectively “received data”).

In an embodiment, a stored inventive, multi-target detection andlocalization process comprising instructions (stored electronic signals)is then executed by computer 100 to complete initial signal processingof the received data. Thereafter, the computer 100 executes furtherstored instructions that are a part of the inventive process to completesteps in sets of different RF signal profiles at each rotation positionof the antenna mast.

In an embodiment, the micro-controller 103 may execute the sameinstructions for each RF signal profile at each rotational position tocomplete one full rotation.

To account for unwanted reflections (i.e., clutter) from stationaryobjects/targets, such as rocks and rubble, such reflections may beelectronically detected and separated from reflections that originatefrom trapped individuals that are moving (though sometimes the movementis slight). The movement and vibration data that is part of the receiveddata can be used to aid false-positive detection of stationaryobjects/targets. The multi-target detection and localization processcomprises full signal processing on all received data for each RF signalprofile and all rotation positions.

In an embodiment, detection results of multiple targets, their vitalsigns and 3D locations may be displayed on display 101 and/or beforwarded or sent to a drone or mobile robot controller 111.

Experimental Set-Up

In an experiment conducted by the inventors a high-performance universalsoftware radio peripheral (USRP) by National Instruments (NI) whichincludes 2×2 MIMO transceivers or four-channel superheterodyne receiversand an onboard field-programmable gate array (FPGA) were used as anexemplary, inventive radar-based life detection system (see FIG. 4).

The NI USRP 2944-R transmitter-receiver (transceiver) had a tunablebandwidth of nearly 6 GHz with frequency range of 10 MHz to 6 GHz withsignal bandwidth of 160 MHz on the carrier frequencies, with two fullduplex channels. The USRP used a powerful Xilinx Kintex 7-410T FPGA foradvanced digital signal processing (DSP) and was controlled via a hostcomputer through PCIe® Gen3 and 10 Gigabit Ethernet for maximum datastreaming bandwidth of 200 MS/s. The programming and control of thisUSRP was done via the host computer using LabVIEW® and LabVIEW® FPGAModule (National Instruments—Austin, Tex.).

The antenna used was a 2 GHz to 11 GHz printed circuit board (PCB) LogPeriodic (LP) antenna model number WASVJB suitable for frequency sweepsand other broadband applications.

The experimental radar was setup in a bistatic, CW configuration forsimultaneous transmitting and receiving.

The inventors generated an exemplary waveform for the radar using aLabVIEW program on the host computer and constantly streamed this datato the USRP transceiver to be transmitted. In full duplex mode, thereceiver of the USRP simultaneously received the reflected signals andconstantly streamed the data representing the reflections back to thehost computer. The host computer executed instructions that functionedas a signal mixer by, for example, multiplying the transmitted signalwith the complex conjugate of the received signal to detect thefrequency difference between the two signals. Thereafter, the hostcomputer executed instructions to complete an inventive, multi-targetdetection and localization process. In an embodiment, one such processthat was competed comprised a short-time Fourier transform (STFT) andtime frequency analysis (TFA) for detecting and displaying movement of atarget (e.g., trapped individual).

In an embodiment, to more precisely detect the movement of a target, RFsignals may be represented by I/Q data where I is the in-phase signalcomponent and Q is the quadrature signal component. In more detail, eachsample of a signal to be generated or measured may be characterized bycomputing a peak amplitude times cosine of some phase angle—A·cos(ϕ).Instead of looking at the signal as a flat curve in two dimensions ofamplitude and time, the inventors represent the signal as a spiral inthree dimensions of amplitude, phase, and time. The I/Q data is just atranslation of amplitude and phase data from a polar coordinate systemto the cartesian coordinate system. Equation (1) may be used fortranslating I/Q signals between polar and rectangular form:

A=√{square root over (I ² +Q ²)}

ϕ=tan⁻¹(Q/I)

I=A·cos(ϕ)Q=A·sin(ϕ)  (1)

where A is the amplitude, ϕ is the phase, I is the real original signal,and Q is the real signal phase shifted by −90°. Equation (2) is theEuler form representation of the signal from I/Q or amplitude and phase:

A·e ^(iϕ) =A·(cos(ϕ)+i·sin(ϕ))=1+Qi  (2)

FMCW Radar

A CW radar can detect movements of a target through shifts in thefrequency due to the Doppler Effect, but is unable to determine therange to the target. FMCW radar is an extension of a CW radar where thefrequency of the transmitted signal is modulated and changing in time.As such, the frequency of the signal increases or decreasesperiodically. This enables the detection of both relative velocity andrange to the target. The frequency of a transmitted signal is known andwhen a reflected signal is received the change in frequency is delayeddue to time of flight to the target and back. FIG. 5 illustrates theprincipals of ranging with a saw tooth linear FMCW radar.

Equation 3 calculates the range to target from a linear FMCW radar:

$\begin{matrix}{R = {\frac{c \cdot {{\Delta \; t}}}{2} = \frac{c \cdot T_{s} \cdot {{\Delta \; f}}}{4B}}} & (3)\end{matrix}$

where R is the range to target in meters, T_(s) is sweep time inseconds, Δt is delay time in seconds, Δf is the instantaneous measuredfrequency difference in Hz, and B is the sweep bandwidth in Hertz (Hz).If the target has a radial velocity, the Doppler frequency shift canalso be measure and used to calculate the velocity using equation (4):

$\begin{matrix}{f_{d} = {\frac{2v_{r}}{\lambda} = {\frac{2{v \cdot \cos}\; \theta}{\lambda} = \frac{\left( {2{v \cdot \cos}\; \theta} \right)f_{T}}{c}}}} & (4)\end{matrix}$

The sweep time can be determined based on the time needed for the signalto travel the unambiguous maximum range. In general, for an FMCW radarsystem, the sweep time should be at least 5 to 6 times the round triptime of the maximum range.

Range resolution of a linear FMCW radar defined as the minimum distancebetween two targets where the radar can differentiate between the two isexpressed as:

Δr=c/2B  (5)

The linearly frequency modulated transmitted signal created by thewaveform generator (host) can be expressed as:

s _(T)(t)=A _(T)(t)·cos(ϕ_(T)(t)),

−T _(s)/2≤t≤T _(s)/2,

ϕ_(T)(t)=2πf _(c) ·t+πB/T _(s) ·t ²  (6)

where A_(T)(t) the amplitude and HO is the phase of the transmittedsignal at time t and f_(c) is the sweep center frequency in Hz. Thes_(T)(t) sweeps from f_(c)−B/2 to f_(c)+B/2 in T_(s) seconds and isradiated toward the target by the transmitting antenna and a sample ofit is also passed through a multiplier (mixer).

The reflected signal from the target may be received by a receivingantenna and enters the same mixer with a time delay of T seconds.Received signal is mixed with a copy of the transmitted signal whichresults in difference and sum of frequencies of the signals. Sum term isabout twice the carrier frequency and is filtered out. Difference termis of a lower frequency, usually few kHz, and contains the informationabout the target. The mixed signal can be expressed as:

$\begin{matrix}{{s_{M}(t)} = {{A_{M}(t)} \cdot {\cos \left( {2{\pi \left( {{\frac{B\tau}{T_{s}}t} - \frac{B\tau^{2}}{2T_{s}} + {f_{c}\tau}} \right)}} \right)}}} & (7)\end{matrix}$

The first term in the cosine function in (7) is the frequency of themixed signal and is the difference of the transmitted and receivedfrequency. This is also known as the beat frequency. The beat frequencyis directly related to the range of the target as expressed by (7). Iftarget is moving the beat frequency will in turn be modulated based onthe Doppler frequency shifts. The next two terms in the cosine functionin (7) correspond to the phase of the mixed signal. This phase angle canalso be used to extract target's range information. The second argumentwith τ² is called the residual video phase, it is very small and canoften be ignored. On the other hand, the third term in the cosinefunction of (7) can be expanded as:

$\begin{matrix}{{f_{c}\tau} = {{f_{c}\frac{2R}{c}} = \frac{2R}{\lambda}}} & (8)\end{matrix}$

where λ is the wavelength of the sweep center frequency f_(c). It ispossible to detect very small changes to the range of the target withinthe unambiguous range of λ/2 using the phase. This resolution depends onradar's phase noise and closely located targets cannot be resolvedseparately. An exemplary linear FMCW radar system operating at f_(c) of5 GHz would have a half-wavelength of 30 mm. With the assumption thatone-degree resolution on measurement of phase angle is possible, aninventive system would have a theoretical minimum detectable movement ofabout 83 μm.

Experimental Results

The inventors used the Phased Array System Toolbox™ from MATLAB® to testthe theoretical range and movement detection capabilities of aninventive, ideal linearly FMCW radar system. Phased Array SystemToolbox™ provides algorithms and apps for the design, simulation, andanalysis of sensor array systems in radar, wireless communication, EW,sonar, and medical imaging applications. The inventors implemented aninventive, linear FMCW radar system operating at center frequency of 5.6GHz (wavelength of 53 mm) with sweep bandwidth frequency of 150 MHz,providing us with 1 m range resolution. The system was setup with amaximum range of 50 m and a sweep time of 1.83 μs. The inventive radarsystem was modeled to be stationary and parallel to the ground at theheight of 50 cm. A target was modeled at the same height in the line ofsight of the radar system at the range of 10 m with a periodic movementtoward to and away from the radar on the plane of radar's line of sight.The target was simulated to move ±200 μm at the frequency of 0.3 Hz forbreathing in addition to amplitude modulation of ±100 μm at thefrequency of 1.5 Hz for heartbeats. The transmitted signal was mixedwith the reflections received. The beat frequency was estimated throughroot MUSIC (MUltiple Signal Classification) algorithm.

The relative changes to the phase of the detected beat signal providedclear and precise range deviations related to the micro-movements. FIGS.6A to 6C graphically present experimental results produced by aninventive system.

USRP Preliminary Results

The inventors experimented and used LabVIEW® NI-USRP API, USRP RIOInstrument Design Library (IDL), and LabVIEW® FPGA Module in testing ofan inventive CW and FMCW radar system operating at 4 GHz for target andmovement detection. The inventors were able to detect and display themicro-Doppler effects of a multi-speed rotating metal fan at 1 meterfrom the FMCW radar system operating at 4 GHz. The inventors were ableto detect and visualize the effects from four different operationalstages of the fan movement. FIG. 7 depicts the frequency shifts as thefan transitions from off to low, medium and maximum speed to off again.

Using the same setup, the inventors were also able to detect movementrelated to breathing using our radar from an individual seated 2 metersfrom the system by analyzing the relative phase shifts on the detectedbeat frequency.

It should be understood that the foregoing description only describes afew of the many possible embodiments that fall within the scope of theinventions.

For example, in additional embodiments, an inventive system may comprisean FPGA that includes 1 Gigabit of dynamic random-access memory andonboard flash memory. This allows the inventive system to transfer awaveform into the onboard memory once and continuously transmit itdirectly from the FPGA, thereby reducing the processing required by acomputer, for example. This also enables the incorporation of digital RFmixers on the FPGA which further reduces the signal processing requiredby the host computer.

Numerous changes and modifications to the embodiments disclosed hereinmay be made without departing from the general spirit of the invention,the scope of which is best defined by the claims that follow.

1. A method for detecting vital signs of a trapped or confinedindividual comprising: transmitting radio frequency signals towards thetrapped or confined individual from a fixed, rotating transmitter;changing the polarity of one or more of the transmitted signals;receiving one or more reflected signals from the trapped or confinedindividual at one or more rotating receivers, each reflected signalcorresponding to a transmitted signal; and completing a short-timeFourier transform and time frequency analysis to detect movement of thetrapped or confined individual based on the received signals.